The present invention relates to a communications network comprising a plurality of transmitting stations and receiving stations for transmitting and receiving signals, said transmitting stations being adapted for transmitting a data signal as a series of data packets, wherein a data packet is scheduled to be transmitted by use of an available transmission resource, and said receiving stations being adapted for transmitting a reservation indicator for reception by transmitting stations. The invention relates further to a corresponding communications method, to a transmitting station and to a receiving station for use in such a communications network.
The growth of wireless internet, and text, picture and video messaging services suggest that 3G and next-generation wireless communications, must adequately support a plurality of packet data services, with bursty traffic characteristics, heterogeneous Quality of Service (QoS) requirements, and traffic load asymmetry both spatially and between the uplink (UL) and downlink (DL) in cellular mobile communications. In order to provide the required QoS support for real-time services and dynamically schedule the bursty traffic centralised intra-cell scheduling is considered the best strategy. Also, to achieve a high trunking and spectral efficiency, 100% frequency re-use is also considered essential. However, centralised intra-cell scheduling, although nearly ideal in the absence of inter-cell interference, fails in the presence of uncontrolled inter-cell interference in a cellular mobile environment. This situation is exacerbated in TDMA systems, which have a higher SIR requirement than CDMA systems, and even worse still in TDMA TDD systems, where there is the potential for significant intercell interference from mobile-station (MS)-to-mobile-station interference.
Coordinating transmissions in neighbouring cells, in a centralised manner, is one way that has been proposed to combat this problem, but it involves significant overhead over the air-interface. In particular, information of the link-gains between each MS in a cell to all MSs and BSs (base stations) in neighbouring cells, needs to be signalled to the network to mitigate MS-to-MS interference (in TDD) and MS-to-BS/BS-to-MS interference (in both TDD and FDD), respectively. This overhead could compromise capacity.
Another approach that has been proposed in H. Haas et al. “Interference diversity through random time slot opposing (RTO) in a cellular TDD system”, Proc. IEEE VTC 2002-Fall, Vol. 3, 24-28 Sep. 2002, pp. 1384-1388 is a ‘passive’ distributed strategy involving slow dynamic channel allocation, such as frequency hopping and slot hopping, does not require any overhead and which averages out the intercell interference. However, this approach cannot react to mitigate sudden increases in interference and therefore its performance is compromised.
US 2002/0041584 A1 discloses a method allowing effective avoid asynchronous interference that occurs in the area where different cells overlap. In a TDMA system, a base station desires of using a channel transmit an interference check signal at a slot corresponding to each of transmission and reception timings on the channel to check whether asynchronous interference occurs on the channel. A mobile station determines whether asynchronous interference occurs on the channel, based on a plurality of error packet reception results on the channel. When asynchronous interference occurs, the mobile station transmits an interference notification signal to the base station. The base station, when receiving an error packet or the interference notification signal, determines that asynchronous interference occurs, and selects another channel to avoid asynchronous interference.
U.S. Pat. No. 6,400,698 B1 discloses a state machine and random reserve access protocol for TDMA packet data mobile stations.